In addition, the board’s general counsel said an inquiry found evidence that a Walmart spokesman, appearing on national television, had unlawfully threatened employees who were considering taking part in the protests.

While the board authorized the filing of a complaint asserting violations of workers’ rights, no complaint was filed on Monday. The board counsel’s office said it would give the parties a chance to reach a settlement.

Walmart denied the accusations, and it called the board’s steps “procedural.”

The board’s general counsel was investigating accusations made against Walmart stemming from protest activities planned last year for Black Friday, among others.

The scope of the accusations was wide, spanning activities in more than a dozen states, and according to the United Food and Commercial Workers union, it covered actions taken against about 100 Walmart employees.

“It’s a major case in terms of the number of stores,” said James J. Brudney, a professor at Fordham University Law School. “And it has a national scope in terms of unlawful threats and terminations.”

Last year, a union-backed group called Our Walmart organized protests at 1,000 Walmart stores in 46 states, a spokeswoman said. Thousands of people participated, demonstrating against retaliation against workers and in support of higher wages, although the company asserted that many were not employees.

In advance of that day of heavy discounts and widely publicized protests, David Tovar, a Walmart spokesman, said on CBS News, “If associates are scheduled to work on Black Friday, we expect them to show up and to do their job, and if they don’t, depending on the circumstances, there could be consequences.”

A news release distributed by the board counsel’s office said Mr. Tovar “threatened employees with reprisal” on two national television broadcasts. The general counsel also asserted that Walmart “unlawfully threatened,” disciplined or fired employees for engaging in strikes or protests in more than a dozen states, including California, Colorado, Texas and Massachusetts. The board also said that Walmart disciplined or fired employees for activities other than strikes in four states.

A union spokeswoman said that at least 43 workers were disciplined and at least 23 were fired.

Whether employees are unionized or not, federal law, under the National Labor Relations Act, protects certain activities, like protesting or organizing for better wages or working conditions.

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In a statement, a Walmart spokesman strongly disagreed with the general counsel’s move.

“This is just a procedural step and we will pursue our options to defend the company because we believe our actions were legal and justified,” said Kory Lundberg, the spokesman.

“It’s important to note that there has not been one decision in the last five years by the N.L.R.B. or by a court finding that Walmart violated the National Labor Relations Act,” Mr. Lundberg said. “That is because we take our obligations under the act very seriously and we train our managers accordingly.”

In a conference call with reporters Monday about planning for another round of protests this year on Black Friday, during which the labor board’s complaint was first announced, several labor activists and union leaders celebrated the board’s decision, including Joseph Hansen, the president of the United Food and Commercial Workers.

“In this morning’s Cleveland Plain Dealer, a Walmart spokesman said the company had a very strong anti-retaliation policy,” Mr. Hansen said. “Yet today, the government confirmed it will prosecute Walmart for illegally firing and disciplining workers who just exercised their rights. Quite frankly, enough is enough.”

The article in The Plain Dealer was not primarily about retaliation, but about wages. The article described a holiday food drive at a Walmart in nearby Canton, Ohio, which included a sign that said, “Please donate food items here so associates in need can enjoy Thanksgiving Dinner.” The article went viral, and activists said it showed that Walmart employees were poorly paid.

Mr. Lundberg said the decision to host the drive was made at the store level to help employees in unexpected hardships, not chronically in need. He said that last year the drive benefited a woman who had stopped receiving child support payments.

In addition to the findings that are at issue between Walmart and the labor relations board, the general counsel’s office said it found no evidence to support other accusations made. Among these findings: the company did not interfere with workers’ right to strike by telling protesters to move off store property in Illinois and Texas, and stores in California and Washington did not illegally change work schedules or coerce employees in retaliation.

During this holiday season, Walmart has been active in a public-relations campaign, including TV ads, featuring the treatment of its workers.

On Monday, Walmart said it promoted more than 350 employees during town hall meetings in Atlanta, Dallas and Phoenix.

A version of this article appears in print on November 19, 2013, on Page B1 of the New York edition with the headline: Labor Panel Finds Illegal Punishments At Walmart. Order Reprints|Today's Paper|Subscribe